Variation in physiological host range in three strains of two species of the entomopathogenic fungus Beauveria

Knowledge of the host range of a biocontrol agent (BCA) is fundamental. Host range determines the BCA's economic potential, as well as the possible risk for non-target organisms. Entomopathogenic fungal strains belonging to the genus Beauveria are widely used as BCA, but our knowledge of their physiological host range is only partial. The aim of this study was to improve our understanding of the physiological host range of three Beauveria strains belonging to two species, B. hoplocheli and B. bassiana. We performed laboratory mortality bioassays to assess their pathogenicity and virulence against nine insect pests, belonging to three orders: Lepidoptera, Coleoptera and Diptera. Mortality rate, mean survival time and mycosis rate were used to estimate virulence. Pathogenicity was assessed as the capacity to cause a disease and induce mortality. Virulence was assessed as the severity of the disease based on mortality rate, mean survival time and mycosis rate. The results of this study revealed significant differences in the physiological host range of the three Beauveria strains tested. The three strains were pathogenic to all Diptera and Lepidoptera species tested. In the case of the Coleoptera, only the B. hoplocheli strain was pathogenic to the white grub Hoplochelus marginalis and only the B. bassiana strains were pathogenic to Alphitobius diaperinus. The B. hoplocheli strain was less virulent on Lepidoptera and Diptera than the two B. bassiana strains. The latter both exhibited very similar virulence patterns. The fact that B. hoplocheli and B. bassiana strains have different host ranges means that they can be used as BCA to target different pests. Impacts on non-target insects across multiple orders cannot be ruled out in the absence of ecological host range studies

Microspectroscopy reveals dust-derived apatite grains in acidic, highly-weathered Hawaiian soils

Dust deposition is an important source of phosphorus (P) to many ecosystems. However, there is little evidence of dust-derived P-containing minerals in soils. Here we studied P forms along a well-described climatic gradient on Hawaii, which is also a dust deposition gradient. Soil mineralogy and soil P forms from six sites along the climatic gradient were analyzed with bulk (X-ray diffraction and P K-edge X-ray absorption near edge structure) and microscale (X-ray fluorescence, P K-edge X-ray absorption near edge structure, and Raman) analysis methods. In the wettest soils, apatite grains ranging from 5 to 30 µm in size were co-located at the micro-scale with quartz, a known continental dust indicator suggesting recent atmospheric deposition. In addition to co-location with quartz, further evidence of dust-derived P included backward trajectory modeling indicating that dust particles could be brought to Hawaii from the major global dust-loading areas in central Asia and northern Africa. Although it is not certain whether the individual observed apatite grains were derived from long-distance transport of dust, or from local dust sources such as volcanic ash or windblown fertilizer, these observations offer direct evidence that P-containing minerals have reached surface layers of highly-weathered grassland soils through atmospheric deposition

Mortality rate of <i>Alphitobius diaperinus</i>, <i>Hoplochelus marginalis</i> and <i>Galleria mellonella</i> treated with <i>Beauveria hoplocheli</i> strain B507, <i>B</i>. <i>bassiana</i> strains I-2960 and I-2961 using 10⁸ conidia.mL^-1 suspensions.

<p>Data presented are means ± SEM, with three replicates of 30 insects for each treatment and each species. Mortality rates were calculated at the time when the mortality rate of the control reached 0.2. For each insect species, a generalized linear model was fitted and pairwise between treatment differences were tested using a likelihood ratio test. Different letters indicate significant differences between treatments (P < 0.05).</p

Kaplan-Meier survival curves for six fruit fly species and <i>Galleria mellonella</i> treated with <i>Beauveria hoplocheli</i> strain B507, <i>B</i>. <i>bassiana</i> strains I-2960 and I-2961 using 10⁶ conidia.mL^-1 suspensions.

<p>Different letters indicate significant differences between treatments within an insect species (log-rank test, P < 0.05 after Sidak’s correction). Crosses indicate censored data.</p

Mycosis rate of six fruit fly species and <i>Galleria mellonella</i> treated with <i>Beauveria hoplocheli</i> strain B507 and <i>B</i>. <i>bassiana</i> strains I-2760 and I-2761 using 10⁶ conidia.mL^-1 suspensions.

<p>Data presented are means ± SEM, with three replicates of 30 insects for each treatment and each species. Mycosis rates were calculated using the percentage of cadavers showing external fungal growth out of the total number of tested insects. For each insect species, a generalized linear model was fitted and pairwise between treatment differences were tested using a likelihood ratio test. Different letters indicate significant differences between treatments (P < 0.05).</p

Kaplan-Meier survival curves for <i>Alphitobius diaperinus</i>, <i>Hoplochelus marginalis</i> and <i>Galleria mellonella</i> treated with <i>Beauveria hoplocheli</i> strain B507 and <i>B</i>. <i>bassiana</i> strains I-2960 and I-2961 using 10⁸ conidia.mL^-1 suspensions.

<p>Different letters indicate significant differences between treatments within an insect species (log-rank test, P < 0.05 after Sidak’s correction). Crosses indicate censored data.</p

Insects used in bioassays.

<p>Insects used in bioassays.</p

Variation in physiological host range in three strains of two species of the entomopathogenic fungus <i>Beauveria</i>

<div><p>Knowledge of the host range of a biocontrol agent (BCA) is fundamental. Host range determines the BCA’s economic potential, as well as the possible risk for non-target organisms. Entomopathogenic fungal strains belonging to the genus <i>Beauveria</i> are widely used as BCA, but our knowledge of their physiological host range is only partial. The aim of this study was to improve our understanding of the physiological host range of three <i>Beauveria</i> strains belonging to two species, <i>B</i>. <i>hoplocheli</i> and <i>B</i>. <i>bassiana</i>. We performed laboratory mortality bioassays to assess their pathogenicity and virulence against nine insect pests, belonging to three orders: Lepidoptera, Coleoptera and Diptera. Mortality rate, mean survival time and mycosis rate were used to estimate virulence. Pathogenicity was assessed as the capacity to cause a disease and induce mortality. Virulence was assessed as the severity of the disease based on mortality rate, mean survival time and mycosis rate. The results of this study revealed significant differences in the physiological host range of the three <i>Beauveria</i> strains tested. The three strains were pathogenic to all Diptera and Lepidoptera species tested. In the case of the Coleoptera, only the <i>B</i>. <i>hoplocheli</i> strain was pathogenic to the white grub <i>Hoplochelus marginalis</i> and only the <i>B</i>. <i>bassiana</i> strains were pathogenic to <i>Alphitobius diaperinus</i>. The <i>B</i>. <i>hoplocheli</i> strain was less virulent on Lepidoptera and Diptera than the two <i>B</i>. <i>bassiana</i> strains. The latter both exhibited very similar virulence patterns. The fact that <i>B</i>. <i>hoplocheli</i> and <i>B</i>. <i>bassiana</i> strains have different host ranges means that they can be used as BCA to target different pests. Impacts on non-target insects across multiple orders cannot be ruled out in the absence of ecological host range studies.</p></div

Mortality rate of six fruit fly species and <i>Galleria mellonella</i> treated with <i>Beauveria hoplocheli</i> strain B507, <i>B</i>. <i>bassiana</i> strains I-2960 and I-2961 using 10⁶ conidia.mL^-1 suspensions.

<p>Data presented are means ± SEM, with three replicates of 30 insects for each treatment and each species. Mortality rates were calculated at the time when the mortality rate of the control reached 0.2. For each insect species, a generalized linear model was fitted and pairwise between treatment differences were tested using a likelihood ratio test. Different letters indicate significant differences between treatments (P < 0.05).</p